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Ionic Bonding,Evidence for the existence of ions,X ray diffraction Electron density map of NaCl. These maps show the,likelihood of finding The ions are discrete or. electrons in a region separate because the,electron density falls to zero. The contours are lines of between the ions,equal electron density. The electron density map, The maps show that for NaCl does not however show the. The ions are arranged in a edge of the ion and so it is. regular pattern difficult to measure the,radius of the ion from an. The chloride ions are larger than electron density map. the sodium ions,Physical properties of Ionic Compounds. high melting points there are strong attractive forces between the ions. non conductor of electricity when solid ions are held together tightly and can not move. conductor of electricity when in solution or molten ions are free to move. brittle easy to cleave apart, A little force will push the ions along and ions will be next to similar ions There will be a force. of repulsion between like ions pushing the layers apart. Migration of ions,Blue colour of, Cu2 ions Yellow colour of A drop of potassium Manganate. migrate to the CrO42 ions solution which is purple is. negative migrate to the placed on moist filter paper on a. electrode positive microscope slide and the ends,electrode of the slide are connected to a. 24 V DC power supply After ten,minutes the purple colour of the. MnO4 ion has migrated to the,positive electrode,N Goalby chemrevise org 2. Covalent Bonding, A covalent bond strong and is caused by the electrostatic attraction. between the bonding shared pair of electrons and the two nuclei. The strength of covalent bond can be demonstrated by the high melting points of giant atomic. structures like diamond and graphite They have high melting points because they contain many. strong covalent bonds in a macromolecular structure It takes a lot of energy to break the many. strong bonds,The X ray diffractions for the hydrogen. molecule show high concentration of negative,charge between H nuclei This negative charge. is strongly attracted by both nuclei so attractive. interactions exceed repulsive ones, In a covalent compound there is significant electron. density between the atoms,Electron Configuration Diagrams. Effect of multiple bonds on bond strength and length. Nuclei joined by multiple i e double and triple bonds have a greater electron density between them. This causes an greater force of attraction between the nuclei and the electrons between them resulting in a. shorter bond length and greater bond strength,N Goalby chemrevise org 3. Dative Covalent bonding,A Dative covalent bond forms when the O. shared pair of electrons in the covalent bond,come from only one of the bonding atoms A. dative covalent bond is also called co ordinate H,Common examples you should be able to. draw that contain dative covalent bond e g,NH4 H3O NH3BF3. The ammonium ion NH4,The direction of the arrow,goes from the atom that is. providing the lone pair to the,atom that is deficient. H Two aluminium chloride,Cl AlCl3 molecules join,x together through two dative. bonds to form the dimer,Cl Al x Cl Al2Cl6,Cl Al Cl Cl. The dative covalent bond acts like,an ordinary covalent bond when. thinking about shape so in NH4 Cl,the shape is tetrahedral. N Goalby chemrevise org 4,Shape of molecules,Name No No lone Diagram Bond angle Examples. bonding pairs,linear 2 0 Cl Be Cl 180 CO2 CS2 HCN,Trigonal 3 0 Cl Cl 120 BF3 AlCl3 SO3. planar NO3 CO32,Tetrahedral 4 0 H 109 5 SiCl4 SO42 ClO4. Trigonal 3 1 107 NCl3 PF3 ClO3,pyramidal H3O,Bent 2 2 104 5 OCl2 H2S OF2. Trigonal 5 0 F 120 and 90 PCl5,Bipyramidal F,Octahedral 6 0 90 SF6. How to explain shape 1 State number of bonding pairs and lone pairs of electrons. 2 State that electron pairs repel and try to get as far apart as possible or to a. position of minimum repulsion, 3 If there are no lone pairs state that the electron pairs repel equally. 4 If there are lone pairs of electrons then state that lone pairs repel more than. bonding pairs,5 State actual shape and bond angle, Remember lone pairs repel more than bonding pairs and so reduce bond angles by about 2 5o. per lone pair in above examples,N Goalby chemrevise org 5. Occasionally more complex shapes are seen that are variations of octahedral and trigonal. bipyramidal where some of the bonds are replaced with lone pairs You do not need to learn the. names of these but ought to be able to work out these shapes using the method below. Square planar Bond angle 89O Bond angle 89O Bond angles 119 89O. Bond angle 180O, Bond angle 90O Reduced by lone pair Reduced by lone pairs Reduced by lone pair. e g XeF4 e g BrF5 e g I3 e g ClF3 e g SF4 IF4, Xe has 8 electrons in its outer Cl has 7 electrons in its outer I has 7 electrons in its outer. shell 4 F s add 4 more shell 3 F s add 3 more shell 4 F s add 4 more. electrons This makes a total of electrons This makes a total of electrons Remove one electron. 12 electrons made up of 4 10 electrons made up of 3 bond as positively charged This. bond pairs and 2 lone pairs pairs and 2 lone pairs The makes a total of 10 electrons. The means it is a variation of means it is a variation of the 5 made up of 4 bond pairs and 1. the 6 bond pair shape bond pair shape trigonal lone pair The means it is a. octahedral bipyramidal variation of the 5 bond pair. shape trigonal bipyramidal,N Goalby chemrevise org 6. Electronegativity and intermediate bonding,Definition F O N and Cl are the. most electronegative, Electronegativity is the relative tendency of an atom in a covalent bond atoms. in a molecule to attract electrons in a covalent bond to itself. The most electronegative, Electronegativity is measured on the Pauling scale ranges from 0 to 4 element is fluorine and it. is given a value of 4 0,Factors affecting electronegativity. Electronegativity increases across a period as the number of protons increases and the atomic radius. decreases because the electrons in the same shell are pulled in more. It decreases down a group because the distance between the nucleus and the outer electrons increases and. the shielding of inner shell electrons increases,Intermediate bonding. Ionic and covalent bonding are the extremes of a continuum of bonding type Differences in. electronegativity between elements can determine where a compound lies on this scale. A compound containing elements of similar electronegativity and hence a small. electronegativity difference will be purely covalent. A compound containing elements of very different electronegativity and hence a. very large electronegativity difference 1 7 will be ionic. Formation of a permanent dipole polar covalent bond The element with the. A polar covalent bond forms when the elements in the bond have different electronegativity in a. electronegativities Of around 0 3 to 1 7 polar compound will. be the end, When a bond is a polar covalent bond it has an unequal distribution of. electrons in the bond and produces a charge separation dipole H Cl. Polar and Non Polar molecules,Symmetric molecules, A symmetric molecule all bonds identical and no lone. pairs will not be polar even if individual bonds within. the molecular ARE polar,CO2 is a symmetrical molecule and. The individual dipoles on the bonds cancel out,is a non polar molecule. due to the symmetrical shape of the molecule,There is no NET dipole moment the molecule is. e g CCl4 will be non polar whereas CH3Cl will be polar H. N Goalby chemrevise org 7, Experiment effect of charged rod on polar non polar liquids. In this experiment a charged rod formed by rubbing a. plastic rod is brought close to a jet of liquid flowing from a. If the liquid is polar the jet of liquid will be attracted to the. electrostatic force of the rod The dipoles in the polar molecules will. all align and the negative end will be attracted to the positive rod. or vice versa The stronger the dipole the more the deflection of the. Non polar liquids will not be deflected and attracted to the charged rod. Intermolecular Forces, London Forces London forces occur between all molecular substances and noble gases They do. not occur in ionic substances, London Forces are also called instantaneous induced dipole. dipole interactions They occur between all simple covalent. molecules and the separate atoms in noble gases, In any molecule the electrons are moving constantly and randomly As. this happens the electron density can fluctuate and parts of the. molecule become more or less negative i e small temporary or. transient dipoles form, These temporary dipoles can cause dipoles to form in neighbouring. molecules These are called induced dipoles The induced dipole is. always the opposite sign to the original one,Main factor affecting size of London Forces. The more electrons there are in the molecule the higher the chance that temporary dipoles will form This. makes the London forces stronger between the molecules and more energy is needed to break them so. boiling points will be greater, The increasing boiling points of the halogens down the group 7 series can be explained by the. increasing number of electrons in the bigger molecules causing an increase in the size of the London. forces between the molecules This is why I2 is a solid whereas Cl2 is a gas. The increasing boiling points of the alkane homologous series can be explained by the increasing. number of electrons in the bigger molecules causing an increase in the size of the London forces. between molecules, The shape of the molecule can also have an effect on the size of the London forces Long straight chain. alkanes have a larger surface area of contact between molecules for London forces to form than. compared to spherical shaped branched alkanes and so have stronger London forces. N Goalby chemrevise org 8,Permanent dipole dipole forces. Permanent dipole dipole forces occurs between polar molecules. It is stronger than London forces and so the compounds have higher boiling points. Polar molecules have a permanent dipole commonly compounds with C Cl C F C Br H Cl C O bonds. Polar molecules are asymmetrical and have a bond where there is a significant difference in. electronegativity between the atoms,Permanent dipole forces. occur in addition to London,Hydrogen bonding, It occurs in compounds that have a hydrogen atom attached to one of the three most. electronegative atoms of nitrogen oxygen and fluorine which must have an available lone pair of. electrons e g a O H N H F H bond There is a large electronegativity difference between the. H and the O N F,Always show the lone pair of electrons on the. O F N and the dipoles and all the charges H, Hydrogen bonding occurs in addition to London forces H H. The hydrogen bond should have an bond angle of 180o with one O. of the bonds in one of the molecules, The bond angle is 180O around the H atom because there are Water can form two hydrogen bonds. two pairs of electrons around the H atom involved in the per molecule because the. hydrogen bond These pairs of electrons repel to a position of electronegative oxygen atom has two. minimum repulsion as far apart as possible lone pairs of electrons on it. It can therefore form stronger, Alcohols carboxylic acids proteins amides all can form hydrogen bonds hydrogen bonding and needs more. energy to break the bonds leading to,a higher boiling point. Alcohols form hydrogen bonds This means alcohols have. higher boiling points and relatively low volatility compared to Ice H H. alkanes with a similar number of electrons O,In ice the molecules are held further. apart by the hydrogen bonds than in,liquid water and this explains the lower. density of ice,N Goalby chemrevise org 9,Hydrogen bonding is stronger than the other two. types of intermolecular bonding,The anomalously high boiling points of H2O. NH3 and HF are caused by the hydrogen bonding,Boiling point K. 300 HF H2Te,between these molecules in addition to their. London forces The additional forces require more H2Se SbH3. energy to break and so have higher boiling points HI. PH3 HCl SnH4, The general increase in boiling point from H2S to SiH4. H2Te or from HCl to HI is caused by increasing 100 CH4. London forces between molecules due to an,increasing number of electrons. 25 50 75 100 125,Molecular mass,Solvents and Solubility. Solubility of a solute in a solvent is a complicated balance of energy required to break bonds in the solute. and solvent against energy given out making new bonds between the solute and solvent. Ionic substances dissolving in water,hydration of the ions. When an ionic lattice dissolves in water it,involves breaking up the bonds in the lattice. and forming new bonds between the metal,ions and water molecules. The negative ions are attracted to the,hydrogens on the polar water molecules and. The higher the charge density the greater the hydration. the positive ions are attracted to the oxygen, enthalpy e g smaller ions or ions with larger charges. on the polar water molecules, as the ions attract the water molecules more strongly. Solubility of simple alcohols,The smaller alcohols are soluble in water. because they can form hydrogen bonds C H,with water The longer the hydrocarbon H. chain the less soluble the alcohol C,Insolubility of compounds in water. Compounds that cannot form hydrogen bonds with water molecules e g polar molecules such as. halogenoalkanes or non polar substances like hexane will be insoluble in water. N Goalby chemrevise org 10,Solubility in non aqueous solvents. Compounds which have similar intermolecular, forces to those in the solvent will generally dissolve. Non polar solutes will dissolve in non polar solvents e g Iodine which has only London forces between. its molecules will dissolve in a non polar solvent such as hexane which also only has London forces. Propanone is a useful solvent because it has both polar and. non polar characteristics It can form London forces with some. non polar substances such as octane with its CH3 groups Its. polar C O bond can also hydrogen bond with water O H O C. Metallic bonding, Metals consist of giant lattices of metal ions in a sea of delocalised electrons. Definition Metallic bonding is the electrostatic force of attraction between the. positive metal ions and the delocalised electrons, The three main factors that affect the strength of metallic bonding are. 1 Number of protons Strength of nuclear attraction. The more protons the stronger the bond, 2 Number of delocalised electrons per atom the outer shell electrons are delocalised. The more delocalised electrons the stronger the bond. 3 Size of ion,The smaller the ion the stronger the bond. Metals have high melting points because the strong electrostatic forces between positive ions. and sea of delocalised electrons require a lot of energy to break. Mg has stronger metallic bonding than Na and hence a higher. melting point The Metallic bonding gets stronger because in Mg. there are more electrons in the outer shell that are released to the. sea of electrons The Mg ion is also smaller and has one more. proton There is therefore a stronger electrostatic attraction. between the positive metal ions and the delocalised electrons. and higher energy is needed to break bonds, Metals can conduct electricity well because the delocalised electrons can move through the structure. Metals are malleable because the positive ions in the lattice are all identical So the planes of ions. can slide easily over one another The attractive forces in the lattice are the same whichever ions are. N Goalby chemrevise org 11, 2B Structure ionic metallic molecular and giant covalent macromolecular. You should be able to draw the following diagrams or describe the structure in words to. show the four different types of crystal You should also be able to explain the properties of. these solids,Giant lattices are present in,i ionic solids giant ionic lattices. ii covalently bonded solids such as diamond graphite and silicon IV oxide giant covalent lattices. iii solid metals giant metallic lattices,Ionic sodium chloride. Giant Ionic lattice showing alternate,Na and Cl ions. Giant Covalent diamond Giant Covalent Graphite,Planar arrangement of carbon. Tetrahedral arrangement of atoms in layers 3 covalent bonds. per atom in each layer 4th outer,carbon atoms 4 covalent. electron per atom is delocalised,bonds per atom Delocalised electrons between. Both these macromolecular structures have very high melting points because of strong covalent. forces in the giant structure It takes a lot of energy to break the many strong covalent bonds. Metallic magnesium or sodium,diagram Giant metallic lattice showing close. for any packing magnesium ions,Molecular Ice This is a difficult diagram. Molecular Iodine H H The main point to show is,O a central water molecule. with two ordinary covalent,bonds and two hydrogen, Regular arrangement of I2 H bonds in a tetrahedral. molecules held together by H arrangement,weak London forces H. H H The molecules are held,HO O further apart than in liquid. H H water and this explains the,lower density of ice. N Goalby chemrevise org 12,Carbon Allotropes,Macromolecular Graphite. Macromolecular diamond,Planar arrangement of carbon. atoms in layers 3 covalent,Tetrahedral arrangement of. bonds per atom in each layer,carbon atoms 4 covalent. 4th outer electron per atom is,bonds per atom,delocalised Delocalised. electrons between layers, Diamond cannot conduct electricity because all 4 Graphite can conduct electricity well between. electrons per carbon atoms are involved in layers because one electron per carbon is free and. covalent bonds They are localised and cannot delocalised so electrons can move easily along. move layers,It does not conduct electricity between layers. because the energy gap between layers is too,large for easy electron transfer. Both these macromolecular structures have very high melting points because of strong covalent. forces in the giant structure It takes a lot of energy to break the many strong covalent bonds. Graphene is a new substance that is a one layer of graphite i e 3 covalent bonds per atom and. the 4th outer electron per atom is delocalised, These have very high tensile strength because of the strong structure of many strong covalent. Graphene can conduct electricity well along the structure because one electron per carbon is free. and delocalised so electrons can move easily along the structure. Carbon nanotubes, These have very high tensile strength because of the strong. structure of many strong covalent bonds, Nanotubes can conduct electricity well along the tube. because one electron per carbon is free and delocalised. so electrons can move easily along the tube, Nanotubes have potentially many uses One being the. potential to us as vehicles to deliver drugs to cells. There are delocalized electrons in buckminsterfullerene. N Goalby chemrevise org 13,Bonding and Structure,Bonding Structure Examples. Ionic electrostatic force of Sodium chloride,attraction between Magnesium oxide. oppositely charged ions Giant Ionic Lattice,Covalent shared pair of Simple molecular Iodine. electrons With intermolecular forces London Ice,forces permanent dipoles hydrogen Carbon dioxide. bonds between molecules Water,Covalent shared pair of Macromolecular Diamond. electrons giant molecular structures Graphite,Silicon dioxide. Metallic electrostatic Giant metallic Magnesium Sodium. force of attraction between lattice all metals,the metal positive ions and. the delocalised electrons, Only use the words molecules and intermolecular forces when talking about simple molecular substances. Property Ionic Molecular simple Macromolecular Metallic. boiling and high because low because of high because of high strong electrostatic forces. melting of giant lattice weak intermolecular many strong covalent between positive ions and sea of. points of ions with forces between bonds in delocalised electrons. strong molecules specify macromolecular, electrostatic type e g London structure Take a lot. forces forces hydrogen of energy to break the,between bond many strong bonds. oppositely,charged ions, Solubility in Generally generally poor insoluble insoluble. water good, conductivity poor ions poor no ions to diamond and sand good delocalised electrons can. when solid can t move conduct and poor because move through structure. fixed in lattice electrons are electrons can t move. localised fixed in localised,place graphite good as free. delocalised electrons,between layers,conductivity good ions can poor no ions poor good. when molten move, general crystalline mostly gases and solids shiny metal. description solids liquids Malleable as the positive ions in. the lattice are all identical So the,planes of ions can slide easily. over one another,attractive forces in the lattice are. the same whichever ions are,N Goalby chemrevise org 14.

Ionic bonding is stronger and the melting points higher when the ions are smaller and/ or have higher charges. E.g. MgO has a higher melting point than NaCl as the ions involved (Mg2+ & O2-are smaller and have higher charges than those in NaCl , Na+ & Cl-) Ionic Bonding Ionic crystals have the structure of giant lattices of ions Ionic Radii

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